Nonstructural carbohydrate-balance response to long-term elevated CO2 exposure in European beech and Norway spruce mixed cultures: biochemical and ultrastructural view

Two dominant central European tree species (Fagus sylvatica, Picea abies), in a mixed culture in semi-open glass domes, were used to simulate a forest, significant carbon sink, reaction to long-term elevated CO2 (EC) in a mountainous area (Beskydy Mountains, the Czech Republic). We investigated the effects of EC on soluble carbohydrate levels and spectra. Starch content was evaluated using two methods â biochemical (glucose content after enzymatic hydrolysis) and stereological (starch grains proportion, size and number in chloroplasts). In beech and spruce foliage, only insignificant changes in total soluble carbohydrate levels were observed. In spruce, starch content determined biochemically increased under EC but only an upward trend was detected in beech. The starch, determined stereologically, was also enhanced, although significantly only in beech. In spruce, EC exposure caused comparable starch increases in current-year and previous-year needles, although the former had a higher starch content and numerous larger starch grains regardless of CO2 concentration. In both species, the biochemical determination of carbohydrates exhibited great individual tree uniformity in contrast to large intraspecies variability. No changes in leaf soluble carbohydrates under long-term elevated CO2 demonstrate the ability of studied tree species to efficiently allocate photosynthates among sinks. Thus, no photosynthetic downregulation via carbohydrate level signalling can be expected.

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